Active thermography is a non-destructive evaluation (NDE) technique in which a non-destructive stimulation such as acoustic or electromagnetic energy is applied to a test object. The applied energy induces mechanical vibrations or electromagnetic currents (respectively) in the object, thereby producing an uneven temperature distribution in the object. Structural features and flaws in the object generate localized heat under such stimulation. A resulting temperature topography on a surface of the object is imaged with an infrared camera. Information about defects and the inner structure of the object can be obtained by evaluating the images individually or a time series of such images. Each image may be digitized into picture elements, or pixels, with each pixel representing a small unit area on the surface. These digitized images can then be used for digital displays and for computer analyses, in which a temperature/time series of images may be processed and analyzed by pixel over time and in patterns of pixels over time and/or space. Time series information improves overall sensitivity of the technique, and facilitates the determination of geometric quantities like local coating thickness, wall thickness, or depth of a defect.
Stationary inspection systems are generally used to test articles of manufacture during their production. Mobile systems are often used for field inspections of operational apparatus such as aircraft, power plant equipment, transportation equipment, and the like. Current NDE techniques such as dye penetrant, magnetic particle coatings, ultrasonic stimulation, and eddy current stimulation have various disadvantages in speed, flexibility and/or potential contamination to the articles tested. Improved NDE devices and techniques are needed.